The present invention relates to processes for forming "self-crimped" foamed fibers, and especially to such processes comprising the steps of forming foamed fiber(s) having a plurality of randomly arranged closed and/or open cells distributed asymetrically over a given cross section of the fiber(s), and heating the fiber(s), while preferably maintaining the fiber(s) under a no load condition, to produce crimped, foamed fiber(s). The invention is also directed to novel foamed fiber which is self-crimping, crimped fiber produced by the process, and products employing the novel fiber.
Foamed thermoplastic (and especially polyamide) fibers have been produced, especially for the purpose of being broken (fibrillated) into 3-dimensional structures of interrelated fiber elements. See, for example, U.K. Patent Specification Nos. 1,316,465 (Changani), 1,221,488, 1,296,710, and 1,318,964.
Foamed polyester and polyamide fibers for textile applications are disclosed in DOS No. 2,148,588 (Apr. 5, 1973) (See Example 7). See also Chem. Abstract 90:24692m (1979) of Japanese Kokai No. 78,106,770.
Hollow fibers, also known in the art, contain elongated voids extending long distances or the entire length of the fiber in the longitudial direction. These fibers contain large void volumes and find use in thermal insulation. The elongated voids are generally produced by the use of a modified spinning die.
Crimped fibers are produced by feeding fibers into stuffer tubes and subjecting them to heat and pressure. More specifically, such processes include the step of feeding fibers into a heated tube at a rate higher than the take-up rate of the fibers from the tube to form a "plug" in the tube, the plug being mechanically deformed fibers which constitute the crimped fiber products. See, for example, U.S. Pat. Nos. 3,406,436 and 3,078,542.
Other mechanical deformation processes for forming crimped fibers are also known. U.S. Pat. No. 3,345,718 discloses a process of mechanically deforming fibers by pressing them between pressure rollers. U.S. Pat. No. 3,619,874 and patents cited therein disclose the use of a blade to plastically deform the fiber to produce crimped products. U.S. Pat. No. 3,009,309 discloses a process wherein fibers are heated, fluid jet twisted, quenched and subsequently back twisted to produce crimped fibers. In U.S. Pat. No. 3,156,028, heated fibers are jet propelled onto a textured surface to mechanically deform the fibers to match the working surface contour.
Multicomponent fibers have been used to produce crimped fibers without the need for mechanical deformation. These fibers comprise components having a different thermal shrinkage properties such that when the fiber is subjected to heat, it will crimp due to the different shrinkage characteristic of each component. See, for example, U.S. Pat. No. 3,425,107.
We have discovered novel self-crimping foamed fibers which require no mechanical deformation in order to crimp. To that end, we have discovered a novel process for crimping the foamed fibers which uses only heat to enhance the production of and set the crimps in the foamed product. The crimped, foamed fibers produced by our process can be used, for example, in apparel and carpet, and as thermal insulation, filter material and acoustic insulation.